The geniculostriate system of normal and monocularly deprived squirrel monkeys (Saimiri sciureus) is to be studied using anatomical, electrophysiological and behavioral techniques. Extracellular injections of horseradish peroxidase (HRP) into the lateral geniculatenucleus (LGN) will be used to identify all afferent sources of input to this nucleus. Immunocytochemistry will be used to determine levels of ChAT and DBH in the LGN. Electron microscopy of at least one of these afferent types (chAT-containing) will determine its terminal distribution and targets in order to evaluate its possible role in the LGN. Correlations between electrophysiological, light microscopic and electron microscopic properties of individual neurons will be studies using extracellular recordings and intracellular injections of HRP. Comparisons between deprived and on-deprived neurons at the light and EM levels will be made with particular emphasis focused on whether the deprived neuron have "leaky" membranes or abnormal synaptic arrangement. The visual fields of the monocularly deprived monkeys will be checked using a behavioral perimetry test to determine if squirrel monkeys have a functionally spared monocular segment for the deprived eye. the results of these studies will lead to a more detailed understanding of the microcircuitry and functioning of the LGN in normal and deprived monkeys. Although this research is restricted to the LGN of squirrel monkeys, the knowledge gained from it should also broaden our understanding of the circuitry and function of many thalamic nuclei, how the brain analyzes or modifies sensory information, and whether the LGN plays a significant role in modifying visual signals following neonatal monocular deprivation. Such knowledge should help to gain insight into overall brain mechanisms and help to prevent or correct central nervous system malfunctions caused by abnormal environmental rearing conditions.